8 Bit or 16 bit , sRGB or Pro Photo

Started Sep 11, 2019 | Discussions thread
pixelgenius Senior Member • Posts: 4,224
Re: Here's where 30 bit monitor path can make a BIG difference

technoid wrote:

knickerhawk wrote:

There's no point in asking other questions when you haven't answered the one I asked. Again: why don't you see any difference between the 8-bit encoded version and the 16-bit encoded version using your "high bit display path"? The synthetic gradients in your test image should be the ideal opportunity to see the superiority of the version encoded at a deeper bit depth, yet you don't see any difference even at 800% apparently. Why?

I alluded to the issue of 8 bit monitors that don't have internal LUTs but are dependent on the driver card's LUTs earlier. Here's a bit more detail that may explain what's going on and also explain why pixelgenius and I see no effects with our 30 bit monitors. First, lets do a little math:

What's the deltaE2000 between ProPhoto RGB (30,30,30) and (31,31,31)? Turns out it is only 0.42 with a "perfect" display.

OK, now the problem with card drivers is that they have to skip RGB steps from time to time unless the rare (or impossible w/o internal LUTs in the display) occurrence exists that the LUTs are totally monotonic and never skip values or duplicate them as 8 bit RGB values change from 0 to 255.

So let's look at the case where 31 is skipped. What's the deltaE2000 between (30,30,30) and (32,32,32)? Hey, it's still under 1 coming in at 0.85.

So it should still not be a problem? Right?

But the problem is much worse than that. The controller card's LUTs are calibrated independently. The R, G, and B channels don't follow each other exactly.

So lets examine he case where just the G channel gets bumped up from 30 to 31. One would expect this isn't a problem. But surprise. It is.

The deltaE2000 from (30,30,30) to (30,31,30) is … wait for it …. 2.38!

With in monitor calibration, which usually is 10 bits or more per channel) even an 8 bit video card doesn't have any missing or duplicated steps so the actual error at the monitor is usually close to half a bit. Big improvement right there. Now, make the data path a full 10 bits/channel with no missing codes and reasonably big monitor LUT depth - problem solved.

Conversion of 16 bit to 8 bit neutral RGBs in this kind of system always keeps the R,G, and B values the same on the black and white balls. The largest error from rounding off 16 to 8 bits is deltaE2000 .28.

This is why pixelgenius and I don't see any visual changes.

Yup, great job explaining the math and facts behind what I tried to explain to him as simply as possible (copy and paste):

Because there's no visual difference.

Now will knickerhawk accept it???? 🤯

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